Multiphase transformer.



No. 669,662. Patented Mar. l2, I904.

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MULTIPHASE TRANSFORMER. (Application filed Dec. 14, 1898.)

(No Model.)

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m: Nonms PEYERS 00.. PHOTO-Lindon wAsHmumm u c UNITED STATES PATENTOFFICE.

EDWIN W. RICE, JR, OF SCHENEOTADY, NEW YORK, ASSIGNOR TO THE GENERALELEOTRIO COMPANY, OF NEW YORK.

MULTIPHASE TRANSFORMER.

.SYPEQLI' LCAIIQN forming part cf Letters Patent No. 669,662, datedMarch 12, 1901.

Application filed December l l, 1898. Serial No. 699,219. (No model.)

To all whom it may concern.-

Be it known that I, EDWIN W. RICE, Jr, a citizen of the United States,residing at Schenectady, in the county of Schenectady and State of NewYork, have invented certain new and useful Improvements in MultiphaseTransformers, (Case No. 963,) of which the following is a specification.

My present invention relates to means for transforming three phasealternating currents, and has for its object to provide a transformerhaving a minimum number of primary and secondary windings, the samebeing arranged on a single core of such structure as to permit the useof a minimum am ount of iron.

My invention further relates to means for supplying currents of variablepotential from the secondaries of multiphase transformers toinduction-motors or other translating devices.

My invention Will be more clearly understood by reference to thefollowing description and accompanying drawings, while its scope will beclearly and particularly pointed out in the accompanying claims.

Figure 1 illustrates in diagram a transforming device made in accordancewith my invention, and Fig. 2 illustrates the use of the same for thepurpose of supplying variable-potential three-phase currents to atranslating device.

In transforming three-phase currents by the use of stationary inductionapparatus it is a common practice to employ two separate transformerswith their primaries connected across two sides, respectively, of thethreephase system and with mains connected in a similar manner to thecorresponding secondaries.

Instead of employing separate transformers in the manner described Ihave found that a considerable economy in iron may be secured bylocating the primary and secondary coils on a single core of such anature that the flux due to the action of one primary and itscorresponding secondary may pass through a part of the iron core commonto the magnetic circuit of the other primary and its secondary. Theresultant flux passing through that part of the core common to bothmagnetic circuits is of necessity a resultant of two equal fluxesdiffering in phase from each other by an angle of one hundred and twentydegrees and is therefore equal in value to each of its component fluxes.The portion of the core carrying the resultant flux may therefore be thesame in cross-section as those portions of the core carrying theindividual fluxes, thus effecting a saving in iron over the arrangementemploying separate transformers, but without increasing the core loss.Fig. l illustrates such an arrangement. The two primary coils which areto be connected across two sides of the three-phase system are indicatedat 1 and 2. The corresponding secondary coils are shown at 3 and l. Thelimbs or branches of the magnetic circuit upon which the primaries andsecondaries are wound are shown at 5 and 6. A third and unwound branch 9serves a magnetic shunt or common magnetic return for the magneticfluxes due to each set of transformer-windings and is the same incross-section as those portions of the core indicated at 5 (5, while endpieces 7 8 are arranged to close the magnetic circuits of the threebranches, as shown.

In Fig. 2 I have shown diagrammatically a transformer of the naturedescribed in which the secondaries are tapped at intermediate points andthe terminals led to a suitable controlling device, the function ofwhich is to connect the terminals in a suitable manner to mains feedinga translating device or devices. The threephase supplymains are shown ata, b, and c. The transformer-primaries l and 2 are connected together at10, and leads ll, 12, and 13 are connected, respectively, to theextremities and junction of said coils and supplied with three-phasecurrents from the mains a, b, and c. The corresponding secondary coils 34 are similarly connected together, with leads connected to theirextremities, the junction of the two coils, and to an intermediate pointor points in the individual coils. The leads are shown as connected toterminals 1% to 18 of a controlling-cylinder, (shown in a developedView.) In the first controller position the terminals 15 and 17, whichare connected, respectively,

to the middle points of the secondary coils 4t and 3, and the terminal16, connected to the junction of said coils, are by the action of saidcontroller put in circuit with the three mains 19 20 21, which lead tothe inducing member of the induction-motor M. The terminal 15 isconnected through the contacts 22 and 23 of the controller with the main19, the terminal 16 through the contact 24: with the main 20, and theterminal 17 through the contacts 25 and 26 with the main 21. In thisposition of the controller it will be seen that only a portion of tneelectromotive force generated in the secondary coils 3 and 4.- isimpressed on the motor M. The motor under these conditions is enabled tostart without drawing from the mains an undesirably large current. Asthe motor speeds up the controller-cylinder is shifted to its secondposition, in which the conductors 27 and 28 are substituted for theconductors 22 28 25 26, the conductor 24 still remaining in connectionwith the terminals associated therewith in its first position. In thisnew position it will be evident from inspect-ion that the main terminals14, 10, and 18 of the three-phase secondary coils 3 and e are connecteddirectly to the supply-mains of the induction-motor M, thus impressingthereon the full electromotive force generated by said transformer.

Although I have shown but one intermediate connection for each secondarycoil of the three-phase transformer, it is evident that any desirednumber may be employed without departing from my invention and that theleads connected to said coil may be manipulated through any suitablecontrolling device for putting them in connection with the workcircuit.

Iam aware thatithas been suggested to subdivide the secondaries ofthree-phase transformers; but in all prior arrangements of this sortwith which I am acquainted the number of leads from thetransformer-secondaries to the translating device have usually beenequal to three times the number of working positions of the controller.Nith my improved arrangement, which is not necessarily restricted to usewith the type of transformer shown in the drawings, I am enabled toreduce the number of leads without interfering with the action and tomake the number of leads equal only to twice the number of workingpositions plus one.

What I claim as new, and desire to secure by Letters Patent of theUnited States, is-

1. The combination of a transformer having three legs of equalcross-section two of which are wound with primary and secondary coilswhile the third is unwound and means for-changing the ratio oftransformation of said transformer.

2. The combination of a transformer having three legs of equalcross-section two of which are wound with primary and secondary coilswhile the third is unwound and means for varying the number of effectiveturns of said secondaries.

3. A transformer having three legs of equal cross-section, one of whichis unwound while primary and secondary coils are placed on the othertwo.

4:. A transformer having a core which is traversed by three fluxes oneof which is the resultant of two fluxes differing in phase by onehundred and twenty degrees.

5. A transformer having a core traversed by three equal magnetic fluxesone of which is the resultant of the other two.

6. A three-phase transformer having its secondary windings subdivided soas to obtain more than one ratio of transformation, the number ofconnections with the secondary windings being less than three times thenu mber of ratios of transformation obtainable.

7. A three-phase tranformer having its secondary windings subdivided soas to obtain more than one ratio of transformation, the number ofconnections with the secondary windings being equal to twice the numberof ratios of transformation obtainable, plus one.

8. A three-phase transformer having two secondaries subdivided forobtaining a variable ratio of transformation and leads connected to saidsecondaries equal in number to twice the number of ratios oftransformation obtainable, plus one.

In witness whereof I have hereunto set my hand this 12th day ofDecember, 1898.

EDI/VIN IV. RICE, JR.

Witnesses:

B. B. HULL, M. II. EMERSON.

